Circuit and method for reducing output voltage transients in a voltage mode buck converter

Abstract

A voltage control mode buck converter circuit includes a feedback amplifier providing a comparison signal and a storage circuit in communication with the comparison signal to store a storage comparison signal value. The storage circuit stores the operating conditions for the circuit during normal continuous conduction mode operation in response to sensing a load drop for the circuit. A switching circuit locks the feedback amplifier into the stored operating parameters while the converter circuit operates in non-continuous conduction mode. When the circuit transitions back into the continuous conduction operation mode, the feedback amplifier is already operating at conditions that are compatible with a continuous conduction operation mode.

1. A voltage control mode buck converter circuit comprising:
 a feedback amplifier configured to provide a comparison signal by comparing a feedback signal responsive to an output voltage for the voltage control mode buck converter circuit to a reference signal when in a continuous conduction operation mode of the voltage control mode buck converter circuit; 
 a storage circuit in communication with the comparison signal and configured to store a comparison signal value responsive to the comparison signal in association with an operation mode change for the voltage control mode buck converter circuit which occurs in association with detection of a load change on an output voltage of the voltage control mode buck converter circuit; 
 a switching circuit configured to switch the feedback amplifier to be in communication with a signal responsive to the stored comparison signal value in association with detection of the load change, wherein the feedback amplifier is further configured to be disconnected from the feedback signal and be connected in unity gain and having a non-inverting input of the feedback amplifier connected to receive the stored comparison signal in response to detection of the load change until a time after detection of the load change. 
 
     
     
       2. The voltage control mode buck converter circuit of  claim 1  wherein the operation mode change comprises a change in the voltage control mode buck converter circuit from the continuous conduction mode to a non-continuous conduction efficiency savings mode. 
     
     
       3. The voltage control mode buck converter circuit of  claim 1  wherein the load change comprises at least one of a group comprising a drop in load current greater than a predetermined amount in a given time period and a drop in load current below a predetermined load current. 
     
     
       4. The voltage control mode buck converter circuit of  claim 1  wherein having the feedback amplifier connected in unity gain and having the non-inverting input of the feedback amplifier connected to receive the stored comparison signal preserves the comparison signal prior to the operation mode change while the voltage control mode buck converter circuit is in a non-continuous conduction operation mode. 
     
     
       5. The voltage control mode buck converter circuit of  claim 4  further comprising a duty cycle comparator circuit in communication with the comparison signal, the duty cycle comparator circuit configured to provide a switched signal in response to the comparison signal wherein the switched signal determines at least in part the output voltage of the voltage control mode buck converter circuit when the voltage control mode buck converter circuit is in the continuous conduction operation mode, and the duty cycle comparator circuit being configured in combination with the storage circuit to provide switched signal information to a burst circuit when the voltage control mode buck converter circuit is in the non-continuous conduction operation mode. 
     
     
       6. The voltage control mode buck converter circuit of  claim 1  wherein the time after detection of the load change comprises when the load change triggering the operation mode change is removed from the voltage control mode buck converter circuit whereby the feedback amplifier is reconfigured to operate in the continuous conduction operation mode. 
     
     
       7. A voltage control mode buck converter circuit comprising:
 a feedback line in communication with an output voltage for the voltage control mode buck converter circuit; 
 a first amplifier configured to be in communication with the feedback line and a reference voltage during a continuous conduction operation mode for the voltage control mode buck converter circuit, the first amplifier configured to provide a comparison signal to a comparison line in response to a feedback signal on the feedback line and the reference voltage; 
 a storage circuit in communication with the comparison signal, the storage circuit configured to store a comparison signal value in association with the continuous conduction operation mode prior to a load current drop event; 
 the first amplifier configured to be in communication with a signal corresponding to the comparison signal value after a mode transition from the continuous conduction operation mode to a non-continuous conduction operation mode in response to the load current drop event. 
 
     
     
       8. The voltage control mode buck converter circuit of  claim 7  wherein the storage circuit comprises a sample and hold circuit in communication with the comparison signal configured to store the stored comparison signal value in response to the load current drop event and a digital to analog converter circuit in communication with the sample and hold circuit and configured to provide to the first amplifier the signal corresponding to the comparison signal when the voltage control mode buck converter circuit is in the non-continuous conduction operation mode. 
     
     
       9. The voltage control mode buck converter circuit of  claim 7  wherein the load current drop event comprises at least one of a group comprising a drop in load current greater than a predetermined amount in a given time period and a drop in load current below a predetermined load current. 
     
     
       10. The voltage control mode buck converter circuit of  claim 7  wherein the first amplifier is configured to be disconnected from the feedback line and connected in unity gain and having a non-inverting input of the first amplifier connected to receive the stored comparison signal in response to the load current drop event. 
     
     
       11. The voltage control mode buck converter circuit of  claim 10  wherein having the first amplifier connected in unity gain with the non-inverting input of the first amplifier connected to receive the stored comparison signal preserves the comparison signal prior to conversion of the voltage control mode buck converter circuit to the non-continuous conduction operation mode. 
     
     
       12. The voltage control mode buck converter circuit of  claim 11  further comprising a duty cycle comparator circuit in communication with the comparison signal, the duty cycle comparator circuit configured to provide a switched signal in response to the comparison signal wherein the switched signal determines at least in part the output voltage of the voltage control mode buck converter circuit when the voltage control mode buck converter circuit is in the continuous conduction operation mode, and the duty cycle comparator circuit being configured in combination with the storage circuit to provide switched signal information to a burst circuit when the voltage control mode buck converter circuit is in the non-continuous conduction operation mode. 
     
     
       13. A voltage control mode buck converter circuit comprising:
 a feedback line in communication with an output voltage for the voltage control mode buck converter circuit; 
 a first amplifier configured to be in communication with the feedback line and a reference voltage during a continuous conduction operation mode for the voltage control mode buck converter circuit, the first amplifier configured to provide a comparison signal to a comparison line in response to a feedback signal on the feedback line and the reference voltage; 
 a switching circuit configured to switch the first amplifier to be in unity gain and in communication with a signal responsive to the comparison signal, the switching circuit configured to switch during a mode transition from the continuous conduction operation mode to a non-continuous conduction operation mode in response to a load current drop event. 
 
     
     
       14. The voltage control mode buck converter circuit of  claim 13  wherein having the first amplifier connected in unity gain and in communication with a signal responsive to the comparison signal preserves the comparison signal prior to the operation mode change while the voltage control mode buck converter circuit is in a non-continuous conduction operation mode such that when the voltage control mode buck converter circuit converts back to the continuous conduction operation mode output voltage transients are reduced in the voltage mode buck converter circuit. 
     
     
       15. The voltage control mode buck converter circuit of  claim 14  further comprising a duty cycle comparator circuit in communication with the comparison signal, the duty cycle comparator circuit configured to provide a switched signal in response to the comparison signal wherein the switched signal determines at least in part the output voltage of the voltage control mode buck converter circuit when the voltage control mode buck converter circuit is in the continuous conduction operation mode, and the duty cycle comparator circuit being configured to provide switched signal information to a burst circuit when the voltage control mode buck converter circuit is in the non-continuous conduction operation mode. 
     
     
       16. The voltage control mode buck converter circuit of  claim 13  wherein the switching circuit is further configured to switch the voltage control mode buck converter circuit to be connected according to the continuous conduction operation mode when the load current drop is removed from the voltage control mode buck converter circuit. 
     
     
       17. A method of reducing output voltage transients in a voltage mode buck converter circuit comprising:
 comparing a feedback signal from a feedback amplifier indicative of an output voltage for the voltage mode buck converter circuit to a reference signal to provide a comparison signal; 
 sensing a load drop for the voltage mode buck converter circuit; 
 storing a comparison signal value relating to the comparison signal at about a time of sensing the load drop; 
 locking the feedback amplifier to a signal responsive to the comparison signal value; and 
 providing the signal responsive to the comparison signal value to a feedback amplifier of the voltage mode buck converter circuit and connecting the feedback amplifier in unity gain in response to sensing the load drop. 
 
     
     
       18. A method of reducing output voltage transients in a voltage mode buck converter circuit comprising:
 operating the voltage mode buck converter circuit in a continuous conduction operating condition including comparing a feedback signal from a feedback amplifier responsive to an output voltage for the voltage mode buck converter circuit to a reference signal to provide a comparison signal used at least in part to adjust the output voltage of the voltage mode buck converter circuit; 
 operating the voltage mode buck converter circuit in a non-continuous conduction mode including: 
 storing a comparison signal value responsive to the comparison signal from the continuous conduction operating condition; 
 clamping the feedback amplifier to a signal responsive to the stored comparison signal value; 
 transitioning to operating the voltage mode buck converter circuit in the continuous conduction operating condition including comparing the feedback signal indicative of the output voltage for the voltage mode buck converter circuit to the reference signal to at least in part to adjust the output voltage of the voltage mode buck converter circuit, wherein the clamping and transitioning further comprises switching the feedback amplifier to be in communication with a signal responsive to the stored comparison signal value in association with detection of the load change, disconnecting the feedback amplifier from the feedback signal and connected in unity gain and connecting a non-inverting input of the feedback amplifier to receive the stored comparison signal in response to detection of the load change until a time after detection of the load change. 
 
     
     
       19. A voltage control mode buck converter circuit comprising:
 a feedback amplifier configured to provide a comparison signal by comparing a feedback signal responsive to an output voltage for the voltage control mode buck converter circuit to a reference signal when in a continuous conduction operation mode of the voltage control mode buck converter circuit; 
 a storage circuit in communication with the comparison signal and configured to store a stored comparison signal value responsive to the comparison signal in association with an operation mode change for the voltage control mode buck converter circuit which occurs in association with detection of a load change on an output voltage of the voltage control mode buck converter circuit; 
 wherein the storage circuit is configured to continuously store a comparison signal value responsive to the comparison signal when the voltage control mode buck converter circuit is in the continuous conduction mode; 
 a switching circuit configured to switch the feedback amplifier to be in communication with a signal responsive to the stored comparison signal value in association with detection of the load change; 
 wherein the feedback amplifier is further configured to be disconnected from the feedback signal and be connected in unity gain and having a non-inverting input of the feedback amplifier connected to receive the stored comparison signal in response to detection of the load change until a time after detection of the load change; 
 wherein having the feedback amplifier connected in unity gain and having the non-inverting input of the feedback amplifier connected to receive the stored comparison signal preserves the comparison signal prior to the operation mode change while the voltage control mode buck converter circuit is in a non-continuous conduction operation mode.